Rockwell Automation 1772-LS_LSP,D17726.8.6 PROG/OPER MANUAL-MINI PLC-2/05 - Manual (Page 74)

Timers and Counters
Chapter 8
8Ć7
The Up Counter instruction retains its AC value when:
You change the mode to the remote program.
The rung condition turns false.
A power outage occurs and memory backup is maintained.
Important: Bit 14 of the accumulated value word is set when the accumulated
value either overflows or underflows. when a down counter preset is 000, the
underflow bit 14 will not be set when the count goes below 0.
Down Counter
Purpose: The Down Counter instruction subtracts one from its accumulated
value for each false to true transition of its rung conditions. A count is only
added on a false to true transition, so rung conditions must go from true to false
and back to true before the next count is registered.
010
00
CTD
030
PR 150
AC 000
When the rung condition becomes:
True
Accumulated value decrements by 1.
Bit 14 is set when AC < 000.
Bit 15 is reset when AC < PR; counting continues.
Bit 16 is set and stays set until the rung goes false.
False
Accumulated value is retained.
Bit 14 - no action is taken.
Bit 15 - no action is taken.
Bit 16 is reset.
Counter Reset
Purpose: The Counter Reset instruction resets the up counter down counter
instructions accumulated value and status bits to 0.
010
00
CTR
030
PR 150
AC 000